This invention relates to an improved process for the preparation of polyesters and more particularly to a process for producing sulfo-modified polyesters more rapidly as well as to producing sulfo-modified polyester material having improved properties.
The commercial packaging industry is finding an ever increasing use of polyester material, most important of which is poly(ethylene terephthalate). This polyester has various known qualities which make its use desirable for protecting comestibles including foodstuffs, beverages, medicines and the like, by enveloping in packages, e.g., molded containers. A particular type of molded container finding wide acceptance is the biaxially oriented container used in the beverage industry. Because of the continuing rise in popularity of such packages in recent years, most notably with the poly(ethylene terephthalate) beverage bottle, there is a need for improvement both in the production of such polyester material as well as in the properties of the polyester material and articles formed therefrom.
In particular, any modification to the method of manufacturing polyester material which will provide increased productivity without requiring additional production equipment and at the same time yield a polymer having improved properties would be welcomed by the industry.
A method has now been found for producing sulfo-modified polyesters more rapidly as well as for producing polyesters having improved properties.
Numerous patents disclose sulfonate monomers and copolyesters containing said monomers. See, for example, U.S. Pat. Nos. 3,634,541; 3,779,993; 3,018,272 and the patents cited therein. However, none of these patents disclose the preparation of the improved sulfo-modified polyesters described herein according to the process of this invention.
The sulfo-modified polyesters produced by the process of this invention are characterized by a more rapid build-up of melt viscosity compared to similar polyesters produced by previous methods. These polyesters are also characterized by improved planar stretch ratios relative to a given inherent viscosity. In addition, these polyesters exhibit significantly improved acetaldehyde generation rates relative to a given planar stretch ratio. Moreover, this process enables the production of these polyesters as well as various articles formed therefrom more rapidly and more economically than by previous methods.